The present invention relates to an automatic arc welding method in which the direction of welding is along the direction of the weld line of a joint to be welded, and more particularly the invention relates to an automatic bead height controlling method for controlling the height of a weld beam at a uniform height.
The realization of an unattended automatic welding requires the use of a position sensor and a welding torch position adjusting mechanism for automatically sensing and correcting the position of the welding torch with respect to the two-dimensional deviation of the groove line which varies from moment to moment during the welding operation.
Various sensors for this purpose have been used in the past and they include the contact-type sensors and the non contact-type sensors of the electromagnetic or optical position sensing type. However, since the use of these sensors requires that a sensor or specific device be positioned as a separate member in the vicinity of the welding torch in addition thereto, it is necessary to maintain a predetermined distance between the sensing position and the welding torch position due to the dimensional limitation and thus from the application point of view there are many limitations in that accurate sensing is not ensured, that there is a limitation to the size of objects to be welded and so on.
Furthere, the welding of joints inevitably involves variations of the groove shapes such as groove width and angle and therefore such variations must be sensed to automatically control the welding conditions. It can be said that there has existed in the past no effective sensing means for this purpose and only a method has been proposed in which the groove in front of the arc is picked up by an ITV to detect the groove width. However, this method has not been put in practical use since it is disadvantageous in that the true groove cross-section is not evident although it is possible to detect the width of the groove surface, that the detection accuracy is in any way limited due to a deviation between the sensing position and the arc position, that there is a limitation to the size of objects to be welded as mentioned previously and so on.
In view of these circumstances, the inventors have proposed a method by Japanese Patent Publication No. 57-3462 in which a welding arc itself oscillated within a groove is used as a sensor and the position of a welding electrode is caused to accurately follow the contour within a groove without using any separate sensor. This method is useful in that not only the welding torch is caused to follow the groove line but also the desired information on the groove cross-section just below the arc is provided by the displacement waveform described by the torch.